To calculate power dissipated by the radiator, fully accurate temperatures are probably not needed, but the sensors should have the same bias, if any is present.
What I believe the High Flow NEXT does, is:
- determine when the computer is off
- allow the loop to settle to ambient
- then using the higher quality/calibrated sensor in the High Flow NEXT as the source
- apply an offset to the remote temperature sensor to equalize the values
In order to do this, the High Flow NEXT requires 5V from the USB connection while the computer is off.
The procedure outlined above is pure speculation on my part, so take it for what it's worth.